There has been a critical temperature indicator of a typical prior art that can be obtained as a commercial name “MONITOR MARK™” of 3M.
As shown in FIG. 1, the critical temperature indicator 10 includes an indicating material or development material layer 11 diffused with being reacted or melted at or above a predetermined temperature and a wicking member or development medium layer 12 absorbing a solvent from the development material layer 11. The development material layer 11 is referred to a temperature sensing layer mixed with ink and fatty acid or paraffin, and the development medium layer 12 is made of absorbing papers, non-woven fibers, etc. a barrier or isolation layer 13 is placed between the development material layer 11 and the development medium layer 12. A first major sheet or supporting layer 14 and an opposing second major sheet or both sided-adhesive tape 15 are in turn arranged on the lower portion of the development material layer 11. An indicating layer 16 includes indication windows to be arranged on the development medium layer 12, in which the indication windows includes larger indicating windows 16′ and smaller indication windows 16″ formed in a longitudinal direction thereon. A transparent layer 17 is positioned on the right of the indication layer 16.
On the other hand, the development medium layer 12, the indication layer 16 and the transparent layer 17 are provided with cutting portions 18 having the same size, respectively, on the same position of their one side. The temperature indicator 10 further includes a supporting layer 14 attached to the both sided-adhesive tape 15, on which the development material layer 11 and the development medium layer 12 are arranged on the supporting layer 14 with the isolation layer 13 positioned there between. Then, the transparent layer 17 is positioned on the indication layer 16 to finish the assembly of the temperature indicator 10.
Therefore, the temperature indicator 10 is attached to a predetermined position of a refrigeration product through the adhesive portion of the both sided-adhesive tape 15, the cutting portion 18 is removed there from and the isolation layer 13 is drawn out between the development material layer 11 and the development medium layer 12 to contact with each other.
Thereafter, the temperature indicator 10 begins to be operated in a manner that the development material 11 including a fluid of fat or paraffin with a pigment ink is melted, infiltrated into the development medium layer 12 and immigrated along the lengthwise thereof to indicate the storage state of the products through the indication windows 16′ and 16″.
But the temperature indicator has disadvantages in that the resultant product size becomes relatively bigger due to the mitigation of the development material in a longitudinal direction, requires a larger power of attention for removing the cutting layer between the development material layer and the development medium and layer. It is difficult to automate the manufacturing of the product. Since the development material is easily exposed to the air atmosphere without being sealed, it must be refrigerated or cooled for over one to two hours below a melting point thereof before being used. If it is used and melted at the state exposed to a normal temperature, some fluid of the development material adheres to the isolation layer when the isolation layer is removed.
Particularly, the development material is slowly migrated as being gradually far away from the starting point. For it, such like strip type of the temperature indicator has a disadvantage in that a error range of the temperature indication time is relatively greater.
Another typical prior art of U.S. Pat. No. 7,232,253 (US Unexamined Publication No. 2004/0240324 published on Dec. 2, 2004) discloses “A time indicator and method of manufacturing same”. The time indicator comprises a first reservoir, a migration medium and activating means for bringing liquid from the first reservoir in contact with the migration medium so that after activation the liquid migrates through the migration medium producing a color change therein. The activating means comprises a second reservoir connected between the first reservoir and the migration medium whereby after activation the liquid travels relatively rapidly from the first reservoir to the second reservoir and then migrates relatively slowly along the length of the migration medium over time.
The patent has some characteristics in that it can measure the time elapse according to its operation and make a visible indication of the product life span. A pressure-rupturable seal or weak seal is formed to isolate a liquid conduit, as the activating means (of a convex dish type) that is constituted to be broken as the first reservoir is pressed with a predetermined amount of force. But the weak seal causes the temperature indicator to be mal-functioned due to the carelessness of users in use. Also, since it must be constructed so that liquid passing through the liquid conduit is contacted with the migration medium, the time indicator has disadvantages in that it is difficult to mass-produce the product due to a stringent configuration such as the weak seal, etc. and to store an enormous volume of products in one unit due to the convex dish type portion.
Another typical prior art of U.S. Pat. No. 6,957,623 discloses “A critical temperature indicator” enabling a visual, irresolvable indication under a critical temperature. The critical temperature indicator includes a transparent housing and a temperature sensitive transformable material operably contained within the transparent housing, which is a mixture of a stabilizer including water, latex, nucleating agent that is preferably ice nucleating active (INA) microorganism. The mixture is translucent prior to exposure of a predetermined temperature and is transformed at a predetermined temperature to render a substantially consistent opaque material, thereby precluding visibility there through and providing a sure visual sign that the indicator has been subjected to the predetermined temperature. Herein, the mixture of the stabilizer has an inherent color and is sealed in the form of a capsule and constituted as means for detecting the thawing and/or refrigeration/freezing of a product, but it has a problem in showing the state transformation of a system. In other words, it is not sure that the critical temperature indication of the system is the exact information of the management state from a time activated under the critical temperature or a time that it is possible to be exposed to a critical temperature, for example from a delivering time and a transformable time of a product having the system.
In order to resolve these problems, another typical prior art of International Patent Application WO/2007/148321 published on Dec. 27, 2007 discloses “An irreversible coolness indicator” which is a type of a critical temperature indicator. The critical temperature indicator comprises a sealed housing having at least one surface, which is transparent and contains a suspension if inorganic monoparticles are suspended in a liquid medium, wherein the suspension undergoes an irreversible detectible change in optical characteristics upon freezing of the liquid medium due to aggregation of the nanoparticles, and wherein the device is provided with means for association thereof with a product, whereby the temperature-threshold indicator device serves to determine whether the product has been exposed to an environment of predetermined coldness.
The critical temperature indicator has features in the simple configuration and the composition of the suspension showing the state transformation at a predetermined color according to a temperature for the refrigeration/thawing detection. But, the critical temperature indicator has some disadvantages in that it is difficult to lower the high manufacturing cost due to the suspension composition, to automate the mass-production thereof and especially to confirm a time to be exposed to the coldness environment. In other words, the critical temperature indicator also fail to show the management states of an activating time under a critical temperature and a time possibly exposed to a critical temperature, whereby the management state from a delivery time to a transformable time of a product cannot be confirmed.
Considering these points, it is preferable if a critical temperature indicator enable the confirmation of a use time point and has an exact operating mechanism there from, and the management state from a delivery time to a transformable time of a product is confirmed.
It is also preferable if a critical temperature indicator reduces the error range of a time exposed to a critical temperature from a time that the development material is first developed in a lengthwise in a strip type of a critical temperature indicator.
It is also preferable if a critical temperature indicator is convenient for the use, adapted to small refrigeration and freezing products and constructed as a simple configuration enabling the mass-production therefor.